Hypothetical reference decoder (HRD) conformance is typically a normative part of video compression standards. A hypothetical reference decoder generally presents a set of requirements on the bitstream. A hypothetical reference decoder verifier may include software and/or hardware and is typically used to verify conformance of a bitstream to the requirements by examining the bitstream, detecting whether any hypothetical reference decoder errors exist and, if so, reporting such errors.
In the context of video compression standards, such as the International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) Moving Picture Experts Group-1 (MPEG-1) Standard, the ISO/IEC MPEG-2 Standard, the ISO/IEC MPEG-4 Standard, the International Telecommunication Union, Telecommunication Sector (ITU-T) H.261 Recommendation, the ITU-T H.263 Recommendation, and the ISO/IEC MPEG-4 Part 10 Advanced Video Coding (AVC) Standard/ITU-T H.264 Recommendation (hereinafter the “MPEG-4 AVC standard”), as well as extensions of the same (e.g., including the extensions of the MPEG-4 AVC Standard such as, for example, the multi-view video coding (MVC) extension and the scalable video coding (SVC) extension), a bitstream is determined to be conformant if the bitstream adheres to the syntactical and semantic rules embodied in the standard. One such set of rules takes the form of a successful flow of the bitstream through a mathematical or hypothetical model of the decoder, which is conceptually connected to the output of an encoder and receives the bitstream from the encoder. Such a model decoder is referred to a hypothetical reference decoder (HRD) in some standards or the video buffer verifier (VBV) in other standards. In other words, the hypothetical reference decoder specifies rules that bitstreams generated by a video encoder adhere to for such an encoder to be considered conformant under a given standard. HRD is typically a normative part of video coding standards and, hence, any bitstream under a given standard has to adhere to the HRD rules and constraints, and a real decoder can assume that such rules have been conformed with and such constraints have been met.
In a first prior art approach, we have previously disclosed and described a hypothetical reference decoder. The hypothetical reference decoder described with respect to the first prior art approach is capable of correcting certain types of hypothetical reference decoder errors in a concatenated bitstream. However, buffer underflow errors cannot be corrected without re-encoding. Therefore, if any buffer underflow error occurs, re-encoding is required, which may lead to other hypothetical reference decoder errors occurring in different places in the bitstream.